Schrodingers Cat is sbserved whilst in the box

• wawenspop

wawenspop

When the cat is poisoned in its box then isn't that an observation? So when we open the box after an hour and see it dead it is the 2nd observation? I cannot see what this thought experiment proves at all BECAUSE an 'observation' was done or not done on the cat before the lid was opened. Its one sided.

People glibly say that the cat was both dead AND alive before we looked at it and pretend this has some deeper meaning. But we all know that it was dead OR alive and not dead AND alive.

If the cat were a quantum particle then the act of killing the cat collapses its state at that time, not later.

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Check out Griffith's "Intro to Quantum Mechanics" chapter 12.4 for more discussion along these lines. I used that section as a reference while writing this post:

Yes, the cat is not in a superposition of alive and dead. Let's take the set up of the experiment to be as follows:

A radioactive atom (the quantum system) is placed near a Geiger counter. When the atom decays following laws of QM, the Geiger counter registers a blip and is rigged to release the poison at that time. No human being or other outside observer is present.

The blip of the counter is indeed the measurement. No human is needed to be present.

To quote Griffith's from page 431 of his quantum book:

Schrodinger regarded [the idea of the cat being in a linear combination of alive and dead] as patent nonsense, and I think most physicists would agree with him. There is something absurd about the very idea of a macroscopic object being in a linear combination of two palpably different states. An electron can be in a linear combination of spin up and spin down, but a cat simply cannot be in a linear combination of alive and dead.

The essence of a measurement, as far as QM is concerned, happens when the quantum system becomes coupled to a classical system. This occurs when the Geiger counter measures the state of the atom. The Geiger counter is, undoubtedly, a classical system and once it interacts with the atom, the measurement is done and the entire system (atom+counter+cat) is in a definite classical state of either dead or alive(radiation not emitted or emitted).

Of course, one can say that the classical system is, fundamentally, described by the laws of quantum mechanics, so why can't it occupy the linear combination of states? The reason is because once you have a system of 10^23 particles, linear combinations become extremely improbable, leaving classical states as the only possible states. This phenomenon is what physicists call decoherence.

The point of the Schrodingers Cat experiment is not to say that quantum mechanics predicts the cat to be both alive and dead at the same time, but instead to point out this link between measurement and the coupling of a quantum system to a classical one.

hi wawenspop!
When the cat is poisoned in its box then isn't that an observation? So when we open the box after an hour and see it dead it is the 2nd observation? I cannot see what this thought experiment proves at all BECAUSE an 'observation' was done or not done on the cat before the lid was opened. Its one sided.

let's examine the experiment in more detail …

something in the box emits a particle with a probability of 50% while the box is closed …

the particle could be used in various ways … for example, it could be allowed to interfere with another such particle, or it could be diverted through gratings or fields before such interference, or it could be allowed to collide with something else and be absorbed but causing a different particle to be emitted which could similarly be diverted etc or interfere with another particle, and so on

in all those cases, the wave function would not collapse, since there would always be the possibility of it interfering with another similar particle …

(obviously if we arrange the experiment so as to check what happened at any stage (like checking which slit an electron went through in the standard double slit experiment), then that would collapse the wave function, so we don't look inside the box )

Schrödinger's point was that there's no essential difference between colliding with another particle etc and colliding with a poison bottle that kills a cat
People glibly say that the cat was both dead AND alive before we looked at it and pretend this has some deeper meaning. But we all know that it was dead OR alive and not dead AND alive.

(actually they should say that the question whether it was dead or alive has no meaning, adn shouldn't be asked)

yes we do know that it was dead or alive … that's the whole point of the paradox …

somewhere in the scale between electron and cat there's a dividing line, and nobody can explain where that dividing line is …

can you say where the dividing line is?

(it's certainly larger than a molecule, since carbon molecules have been observed interfering with each other)
If the cat were a quantum particle then the act of killing the cat collapses its state at that time, not later.

certainly not

a "quantum" cat would be able to interfere with another "quantum" cat …

its wave function would not collapse until we opened the box and looked for "quantum" kittens!

I can sort of see what you both are saying, but my natural instinct is to now do the same experiment for a proper quantum particle.

So we have an electron in superposition in a closed box. A radioactive decay shoots out another particle that... what?

There should be a simple analogous experiment described for a quantum particle.
Its the details of that (proper quantum) experiment I cannot piece together.
I bet I do not get a simple 'thought' experimental procedure reply, because its hard in all honesty...

Is it just me having problems? (I understand Copenhagen i and superposition by-the-way, its this experiment that I do not get. Its so mixed up... IMO)